(1) Field of the Invention
The invention relates to a method of producing a hollow shaft, in particular a camshaft, according to the internal high-pressure forming process (IHF), cams and/or machine elements being mounted on the outer lateral surface of the hollow shaft, in such a way as to be adapted to the use of the latter, in a frictional and/or positive-locking manner and so as to be distributed in functionally correct positions. The machine elements may be, for example, gears, drives, cam plates or the like. A preferred field of application is camshafts for motor vehicle engines.
(2) Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
It is known to produce camshafts for motor vehicle engines by the internal high-pressure forming process (IHF) by a hollow shaft being widened by the action of pressure after the cams have been pushed on. Liquids are preferably used as pressure medium. In this case, the cams which are pushed on are connected to the shaft in a frictional and positive-locking manner (DE 34 09 541 A1). Even if this process proves to be very effective for mounting machine elements and cams on the shaft and is used in practice, shafts produced in this way still have the shortcoming that, at their ends, functional elements separately produced in a further process have to be connected to the shaft. Bolts are inserted into the shaft with an appropriate snug fit and are frictionally connected to the shaft by pins. It is also conventional practice to weld these bolts to the shaft or to press them into place. These bolts either project from the shaft and are provided with a thread in this region or they have an internal thread.
The general trend in mechanical engineering, in particular in the construction of motor vehicle engines, is to reduce the weight with the output being at least the same. To this end, the camshafts have for some time been used as hollow shafts. In this case, the persons skilled in the art have endeavored to produce these hollow shafts in such a way that the requisite machine elements are also connected to the hollow shaft in a highly reliable manner and at a low production cost.
There are applications of hollow shafts in which a connection to drives is necessary at one end or both ends. For this purpose, it is known to configure these machine elements in such a way that they are designed as a sleeve which are pushed onto the shaft and fastened. At the outer end, the machine element is designed as a flange, at which the coupling is effected (DE 38 00 912 A1). In this case, there are shortcomings with regard to the high mechanical production cost for the element, the accurate fit on the shaft and the frictional connection to the shaft. The connection may also be produced by IHF, but all the shortcomings are not removed.
It is known to form the ends of the hollow shaft by rotary swaging or upsetting in such a way that a thickness increase takes place, the inside diameter is reduced and the outside diameter, by material accumulation, is brought to such a size that a machine element mounted in a known manner is fastened. In this case, the end of the shaft is to be upset by an IHF process in such a way that a collar or flange is produced. These process steps can also be carried out by swaging or rotary swaging (DE 197 10 84.8).
All of the known processes for producing elements connected to the hollow shaft for the purpose of coupling or mounting have the disadvantage in common that the process for producing and for connecting said elements to the shaft in a frictional and positive-locking manner requires at least one additional process step. In addition to this there is also the mechanical treatment. For example, joining processes are necessary and subsequent hardening and/or machining. In addition, a machine fit is required, which in turn increases the cost.